Method, apparatus, and system for data transmission and processing in a wireless communication environment

ABSTRACT

According to one aspect of the present invention, a method is provided in which indications of signal quality associated with each of the plurality of user stations are received. Multiple user stations (e.g., a first user station and a second user station) are selected to receive data from a base station based on the indications of signal quality associated with the plurality of the user stations. A first packet is constructed which contains signaling data for the first user station and application data for the second user station. A second packet which contains application data for the first user station is super-imposed upon the first packet. The first and second packets are transmitted simultaneously from the base station to the first and second user stations.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims priority to ProvisionalApplication No. 60/516,996 entitled “Method, Apparatus, and System forData Transmission and Processing in a Wireless CommunicationEnvironment” filed Nov. 3, 2003.

BACKGROUND

1. Field

The present invention relates generally to the fields of wirelesscommunication and information processing, and more specifically to amethod, apparatus, and system for data transmission and processing in awireless communication environment.

2. Background

In recent years, communication systems' performance and capabilitieshave continued to improve rapidly in light of several technologicaladvances and improvements with respect to telecommunication networkarchitecture, signal processing, and protocols. In the area of wirelesscommunications, various multiple access standards and protocols havebeen developed to increase system capacity and accommodate fast-growinguser demand. These various multiple access schemes and standards includeTime Division Multiple Access (TDMA), Frequency Division Multiple Access(FDMA), Code Division Multiple Access (CDMA), and Orthogonal FrequencyDivision Multiple Access (OFDMA), etc. Generally, in a system whichemploys TDMA technique, each user is allowed to transmit information inhis assigned or allocated time slots whereas an FDMA system allows eachuser to transmit information on a particular frequency that is assignedto that particular user. A CDMA system, in contrast, is a spreadspectrum system which allows different users to transmit information atthe same frequency and at the same time by assigning a unique code toeach user. In an OFDMA system, a high-rate data stream is split ordivided into a number of lower rate data streams which are transmittedsimultaneously in parallel over a number of subcarriers (also calledsubcarrier frequencies herein). Each user in an OFDMA system is providedwith a subset of the available subcarriers for transmission ofinformation.

Code division multiple access (CDMA) technology was introduced incellular systems in the early 1990s with the development of the IS-95standard. The IS-95 system has significantly evolved and matured in thelast decade resulting in the enhanced revisions IS-95 A and B in 1994and 1998, respectively. The IS-95-A/B and several related standards formthe basis of the second generation cellular technology which is alsoknown as cdmaOne.

The 3G evolution of cdmaOne consists of a family of standards, known ascdma2000, which first appeared with the publication of the IS-2000Release 0 in 1999. Release A version of IS-2000 was published in mid2000 with the inclusion of additional signaling support for featuressuch as new common channels, QoS negotiation, enhanced authentication,encryption and concurrent services. The cdma2000 system was designed tobe backward compatible with existing cdmaOne networks and voiceterminals.

The IS-2000 standard introduces several new features as compared tosecond-generation (2G) wireless systems. Among those, the introductionof fast forward power control, QPSK modulation, lower code rates,powerful turbo coding, pilot-aided coherent reverse link and support fortransmit diversity are considered the major capacity enhancing featuresin IS-2000.

Even though the IS-2000 standard introduces new features thatsignificantly improve voice capacity and data services, the design wasnot optimized for high speed IP traffic. As a result, a major additionto cdma2000 was accomplished by the introduction of the high rate packetdata (HRPD) system (IS-856) by the end of 2000. The IS-856 standard,also referred to as 1×EV-DO herein, is optimized for wireless high-speedpacket data services. The IS-856 forward link usestime-division-multiplexed (TDM) waveform, which eliminates power sharingamong active users by allocating full sector power and all code channelsto a single user at any instant. This is in contrast tocode-division-multiplexed (CDM) waveform on the IS-95 forward link,where there is always an unused margin of transmit power depending onthe number of active users and power allocated to each user. Eachchannel (Pilot, Sync, Paging and Traffic channels) in IS-95 istransmitted the entire time with a certain fraction of the total sectorpower, while the equivalent channel in IS-856 is transmitted, at fullpower, only during a certain fraction of time.

Due to the TDM waveform of the IS-856 forward link, a terminal isallocated the full sector power whenever it is served, thus no poweradaptation is needed. Rather, rate adaptation is used on the IS-856forward link. In general, the highest data rate that can be transmittedto each terminal is a function of the received SINR from the servingsector. This is typically a time-varying quantity, especially for mobileusers. In order to achieve the highest data rate at each time oftransmission, each terminal predicts the channel condition over the nextpacket for its serving sector based on the correlation of the channelstates. It selects the highest data rate that can be reliably decodedbased the predicted SINR, and then inform the serving sector itsselected rate over the reverse link feedback channel. Whenever thenetwork decides to serve a terminal, it transmits at the most recentselected rate fed back from the terminal. This procedure is referred toas closed-loop rate control.

In a system which employs TDM scheduling for transmission from a basestation to user terminals or user stations (e.g., the current 1×EV-DOdownlink or forward link transmission), the base station transmits asingle packet to a particular user at any given time. As shown in FIG.1, different users are time-division multiplexed, i.e., served atdifferent points in time. In order to maintain fairness, the systemspends a significant amount of time serving users with low SINR. The TDMscheduling forces the base station to allocate bandwidth among differentusers in the same proportion in which it allocates its transmit power todifferent users. While users in poor coverage require a large share ofbase station transmit power, they need only a small fraction of thebandwidth. While the users with low SINR are being served, the systembandwidth is unnecessarily wasted or underutilized. As a result, thesystem throughput is significant reduced by the presence of a few userswith low SINR (poor coverage).

One approach to addressing the above problem is to use the CDM approach,which is to allocate a variable number of code channels to differentusers, and apply power control to the transmission to multiple users inorder to maintain a reliable link to each user. This approach, however,requires dynamic allocation of code channels to different users, as wellas the need to control the power of the different users rapidly enoughto track channel variation. Moreover, it turns out that any form ofbandwidth-partitioning among multiple users on the downlink issub-optimal, from the viewpoint of throughput optimization. As a result,the CDM approach does not provide as much gain in system throughput.

There is therefore a need in the art for a method, apparatus, and systemfor efficient data transmission and processing in a wirelesscommunication environment to improve system throughput and bandwidthutilization. cl SUMMARY

According to one aspect of the present invention, a method is providedin which indications of signal quality associated with each of theplurality of user stations are received. A first user station and asecond user station are selected to receive data from a base stationbased on the indications of signal quality associated with the pluralityof the user stations. A first packet is constructed which containssignaling data for the first user station and application data for thesecond user station. A second packet which contains application data forthe first user station is super-imposed upon the first packet. The firstand second packets are transmitted simultaneously from the base stationto the first and second user stations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a conventional TDM schedulingconfiguration;

FIG. 2 is a block diagram of a communication system in which theteachings of the present invention are implemented;

FIG. 3 is a diagram illustrating a structure of the forward link;

FIG. 4 is a diagram illustrating a structure of a reverse link;

FIG. 5 is a block diagram showing a rate control configuration accordingto one embodiment of the invention;

FIG. 6 shows a block diagram of a scheduler/controller in accordancewith one embodiment of the present invention;

FIG. 7 shows an example of a table containing the variousselection/scheduling criteria, in accordance with one embodiment of thepresent invention;

FIG. 8 is a diagram illustrating a forward link transmission schemeoperated in accordance with one embodiment of the present invention;

FIG. 9 shows an example of a multi-user packet in accordance with oneembodiment of the present invention;

FIG. 10 shows an example of a multi-user packet upon which anotherpacket is superimposed;

FIG. 11 is a flow diagram of a method for data transmission in awireless communication system, in accordance with one embodiment of thepresent invention; and

FIG. 12 is a flow diagram of a method for data processing in a wirelesscommunication system, in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

In accordance with various embodiments of the present inventiondescribed in details below, the inefficiency associated with TDMscheduling can be avoided by serving multiple users (e.g., two users) ata time, one user with high signal quality level (e.g., high SINR) andanother user with low signal quality level (e.g., low SINR), using atechnique known as superposition coding. Employing superposition codingand scheduling improve the system throughput considerably, withoutdepriving the users with low SINR of their fair share of systemresources and throughput.

While the various examples provided herein are directed to a CDMA-basedsystem such as an IS-856 system, it should be understood and recognizedby one skilled in the art that the teachings of the present inventioncan be applied to any communication system which employs TDM scheduling,CDM scheduling, or combinations thereof. According to one embodiment ofthe invention, in a system which includes a base station servingmultiple user terminals or user stations, the base station may selecteither a single user or multiple users (e.g., a pair of users) to serveat any given moment. If the base station selects a single user to serve,it operates just like the current TDM system. If the base stationselects a pair of users to serve, a “multi-user” packet (first packet)is constructed at a low enough data rate so that both users candemodulate. Another packet (second packet) intended for just one of thetwo users is super-imposed upon the “multi-user” packet. The secondpacket is coded in such a manner that it behaves like randominterference to the multi-user packet. In one embodiment, a “multi-user”packet is a single physical layer packet which contains higher layerpayloads belonging to more than one user. The higher layer payloadaddressed to the low SINR user contains application data for that user.The higher layer payload addressed to the high SINR user containssignaling data for the high SINR user. In one embodiment, the signalingdata indicates the coding/modulation parameters of another physicallayer packet that is simultaneously being transmitted to the high SINRuser. Upon receipt of the signaling data embedded in the multi-userpacket, the high SINR user subtracts the contribution of the multi-userpacket from the received signal, and uses the resulting signal toextract the second packet, whose encoding parameters were specified bythe signaling data. Thus, the low SINR user is served by the bulk of themulti-user packet, while the high SINR user is served by the secondpacket that was superimposed on the multi-user packet. Superpositioncoding and scheduling in accordance with various embodiments of thepresent invention are described in greater detail below.

Time-Division-Multiplexed (TDM) Scheduling:

The following concepts and principles are discussed with respect to acommunication system which includes one transmitter (e.g., a basestation) and multiple receivers (e.g., user terminals or user stations,etc.). Let γ_(k) denote the channel SNR of the k^(th) user station (alsocalled k^(th) user herein). Channel SNR of a user can be defined as theSNR of the data symbols received by that user, if the base stationtransmits to that user at full power. Let C(γ) represent the functionthat maps the data symbol SNR γ to the maximum supportable data rate.The maximum supportable data rate is upper bounded by the Shannoncapacity of an AWGN channel with that SNR. i.e., C(γ)≦W log(1+γ). Itshould be noted that C(γ) is an increasing function of the SNR.

For a TDM scheduler that serves the kth user for a fraction α_(k) of thetotal time, the effective data rate of the k^(th) user is given byR_(k)=α_(k)C(γ_(k)). Accordingly, the rate region of the TDM schedulerwith N users can be defined as the set of all achievable rates of allusers in the system, given by:$\left\{ {{\alpha_{1}{C\left( \gamma_{1} \right)}},{\alpha_{2}{C\left( \gamma_{2} \right)}},\cdots\quad,{\alpha_{N}{C\left( \gamma_{N} \right)}}} \right)\left. {{\alpha_{i} \geq 0},{{\sum\limits_{i = 1}^{N}\quad\alpha_{i}} \leq 1}} \right\}$

TDM Schedulers with different fairness criteria operate at differentpoints in the rate region described above. For example, an equal-GOSscheduler may select the time fractions α_(k) such that all users havethe same effective data rate R_(eq). More specifically, an equal-GOSscheduler may select${\alpha_{k} = \frac{{C\left( \gamma_{k} \right)}^{- 1}}{\sum\limits_{i = 1}^{N}\quad{C\left( \gamma_{i} \right)}^{- 1}}},$so that$R_{k} = {\frac{1}{\sum\limits_{i = 1}^{N}\quad{C\left( \gamma_{i} \right)}^{- 1}} \equiv {R_{eq}.}}$

The total throughput of the system is given by the harmonic mean${R_{tot} \equiv {\sum\limits_{k = 1}^{N}R_{k}}} = {\frac{N}{\sum\limits_{i = 1}^{N}{C\left( \gamma_{i} \right)}^{- 1}}.}$

On the other hand, an equal-time scheduler may select${\alpha_{k} = \frac{1}{N}},$so that the effective rate of the k^(th) user is given by${R_{k} = {\left( \frac{1}{N} \right){C\left( \gamma_{k} \right)}}},$and the total system throughput is given by the arithmetic mean${R_{tot} \equiv {\sum\limits_{k = 1}^{N}R_{k}}} = {\frac{1}{N}{\sum\limits_{k = 1}^{N}{{C\left( \gamma_{k} \right)}.}}}$The proportional-fair scheduler, which tries to maximize the sum of thelogarithmic data rates$\sum\limits_{k = 1}^{N}{\log\quad\left( R_{k} \right)}$also coincides with the equal-time scheduler, for the time-invariant(static) channel considered above.

So far, it has been assumed that the channel is static, i.e., that thechannel SNR of the users do not change with time. If the channel is timevarying, the SNR of the users change with time and a dynamic schedulermay be needed that exploits the channel variations. A dynamic TDMscheduler may pick a user to serve at each time slot, depending on thehistory the SNR of all the users up to that time. Suppose T_(k)[n] isthe throughput of the k^(th) user at time slot n. Let U(T) denote theutility function associated with throughput T. The objective of thescheduler is to maximize the total utility function$\sum\limits_{k = 1}^{N}{U\left( {T_{k}\lbrack n\rbrack} \right)}$at each time slot n. It should be noted that the proportional-fairscheduler is a special case, where the utility function is logarithmic.

Given the above objective, the utility-maximizing dynamic TDM scheduleroperates as follows: at the (n+1)^(th) time slot, the TDM schedulerpicks a user with index k, where k is maximizes the expressionΔ_(k) ≡U((1−β)T _(k) [n]+βC(γ_(k) [n]))−U((1−β)T _(k) [n])˜βU′((1−β)T_(k) [n])C(γ_(k) [n]),where β is inversely related to the duration over which the throughputT_(k) is averaged. In the special case of proportional-fair scheduler,the scheduler picks that user with index k, where k maximizes theexpression$\Delta_{k} \approx {\frac{\beta}{\left( {1 - \beta} \right)}{\frac{C\left( {\gamma_{k}\lbrack n\rbrack} \right)}{T_{k}\lbrack n\rbrack}.}}$Once the scheduler picks the user k who is served during the nth timeslot, the throughput of all the users are updated using the equations:T _(k) [n+1]=(1−β)T _(k) [n]+βC(γ_(k) [n]),T _(i) [n+1]=(1−β)T _(i)[n]i≠k.Superposition Coding:

The idea of superposition coding which entails superimposing high rateinformation on low rate information was first discussed by T. Cover,Broadcast Channels, IEEE Transactions on Information Theory, Vol. IT-18,No. 1, January 1972.

For a given set of channel SNR of the N users, superposition coding canbe used to enlarge the rate region associated with TDM scheduling. Ifthe users are indexed in the decreasing order of their SNR, and if thebase station spends a fraction of its power α_(k) on the data destinedto the k^(th) user, then the set of user data rates is given by${R_{k} = {C\left( \frac{\alpha_{k}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{k - 1}\quad\alpha_{i}}} \right)}},{k = 1},2,\ldots\quad,{N.}$

In one embodiment, the above date rates can be achieved as follows. Thebase station encodes the k^(th) user's packet as the codeword c_(k) atthe data rate R_(k) given above. The base station transmits the signal${x = {{\sum\limits_{k = 1}^{N - 1}\quad{\sqrt{\alpha_{k}}s_{k}*c_{k}}} + {\sqrt{\alpha_{N}}c_{N}}}},$where * denotes the scrambling operation with a pseudo-random sequences_(k). The scrambling operation is performed to ensure that thedifferent users' code words appear random relative to each other. At thereceiver of the k^(th) user, the signal y=x+n_(k) is received, where nkrepresents the additive noise from the channel. The k^(th) user firstdecodes the codeword c_(N), which experiences an${{{SINR}\frac{\alpha_{N}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{N - 1}\quad\alpha_{i}}}} \geq \frac{\alpha_{N}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{N - 1}\quad\alpha_{i}}}},$which holds because γ_(k)≧γ_(N) by assumption. Since the rate functionC(.) is monotonically increasing of the SNR, it follows that${{C\left( \frac{\alpha_{N}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{k - 1}\quad\alpha_{i}}} \right)} \geq {C\left( \frac{\alpha_{k}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{k - 1}\quad\alpha_{i}}} \right)}} = {R_{N}.}$In other words, the SNR of the N^(th) codeword c_(N) at the k^(th)receiver is strong enough to be decoder by the k^(th) user. Once, theN^(th) codeword is decoded, the k^(th) user re-encodes the N^(th) user'spacket, and cancels its contribution from the received signal, anddescrambles the received signal with respect to the scrambling sequences_(N−1). The resulting signal may be expressed as follows:${{\sum\limits_{i = 1}^{N - 1}\quad{\sqrt{\alpha_{i}}s_{N - 1}^{- 1}*s_{i}*c_{i}}} + {s_{N - 1}^{- 1}*n_{k}}} = {{\sqrt{\alpha_{N - 1}}c_{n - 1}} + {\sum\limits_{i = 1}^{N - 1}\quad{\sqrt{\alpha_{i}}s_{N - 1}^{- 1}*s_{i}*c_{i}}} + {s_{N - 1}^{- 1}*{n_{k}.}}}$Then the (N−1)^(th) codeword has an${{{SINR}\frac{\alpha_{N - 1}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{N - 2}\quad\alpha_{i}}}} \geq \frac{\alpha_{N - 1}}{\gamma_{N - 1}^{- 1} + {\sum\limits_{i = 1}^{N - 1}\quad\alpha_{i}}}} = {{C^{- 1}\left( R_{N - 1} \right)}.}$

Based on the equation described above, it follows that the (N−1)^(th)codeword may be successfully decoded by the k^(th) user, if k≦(N−1).Similarly, the k^(th) user decodes the packets c_(N), c_(N−1), . . . ,c_(k+1) and c_(k) through successive cancellation, and eventuallyrecovers the data intended for it.

The rate region associated with superposition coding is significantlylarger than that associated with TDM scheduling, when the system hassome users at very high SNRs, and some other users at very low SNRs. Ifall users have nearly the same SNR, then the two rate regions are verysimilar or nearly identical.

Superposition Coding Scheduler:

Unlike the TDM scheduler which is constrained to serve one user at atime, a scheduler which employs superposition coding techniques (alsocalled superposition coding scheduler herein) can serve more than oneusers at a time, or indeed all the N users at the same time. Thesuperposition coding scheduler needs to select a power fractionallocated to the different users at any given time. By setting the powerfraction allocated to certain users to zero, it may serve only a subsetof users at any given time. As described herein, system bandwidth may bebetter utilized for a superposition coding scheduler to serve just twousers at any given time, one with a very high channel SNR, and the otherwith a very low channel SNR.

In any case, the superposition scheduler operating on a time varyingchannel may select the power fractions {α_(k)} that maximize theincremental utility function${{\Delta\left( \left\{ \alpha_{k} \right\} \right)} \equiv {\sum\limits_{k = 1}^{N}\left\lbrack {{U\left( {{\left( {1 - \beta} \right){T_{k}\lbrack n\rbrack}} + {\beta\quad{C\left( \frac{\alpha_{k}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{k - 1}\quad\alpha_{i}}} \right)}}} \right)} - {U\left( {\left( {1 - \beta} \right){T_{k}\lbrack n\rbrack}} \right)}} \right\rbrack}}\quad = {{\sum\limits_{\underset{\alpha_{k} > 0}{k = 1}}^{N}\left\lbrack {{U\left( {{\left( {1 - \beta} \right){T_{k}\lbrack n\rbrack}} + {\beta\quad{C\left( \frac{\alpha_{k}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{k - 1}\quad\alpha_{i}}} \right)}}} \right)} - {U\left( {\left( {1 - \beta} \right){T_{k}\lbrack n\rbrack}} \right)}} \right\rbrack}\quad \approx {\beta{\sum\limits_{\underset{\alpha_{k} > 0}{k = 1}}^{N}{{U^{\prime}\left( {\left( {1 - \beta} \right){T_{k}\lbrack n\rbrack}} \right)}\quad C\left( \frac{\alpha_{k}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{k - 1}\quad\alpha_{i}}} \right)}}}}$subject to the constraints${\alpha_{i} \geq 0},{{\sum\limits_{i = 1}^{N}\alpha_{i}} \leq 1.}$

In the special case of proportional-fair scheduler, the last expressionreduces to${\Delta\left( \left\{ \alpha_{k} \right\} \right)} \approx {\frac{\beta}{1 - \beta}{\sum\limits_{\underset{\alpha_{k} > 0}{k = 1}}^{N}{{T_{k}\lbrack n\rbrack}^{- 1}{{C\left( \frac{\alpha_{k}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{k - 1}\quad\alpha_{i}}} \right)}.}}}}$

As noted before, the scheduler may adopt additional constraints, such asat most two (or in general, at most M<N) of the power fractions α_(i)are non-zero.

Accordingly, the user throughput is updated using the equations${T_{k}\left\lbrack {n + 1} \right\rbrack} = {{\left( {1 - \beta} \right){T_{k}\lbrack n\rbrack}} + {\beta\quad{{C\left( \frac{\alpha_{k}}{\gamma_{k}^{- 1} + {\sum\limits_{i = 1}^{k - 1}\quad\alpha_{i}}} \right)}.}}}$

While significant improvements in system throughput may be achieved bysuperposition coding and scheduling (SC), there are a number ofpractical considerations that may limit the performance gains in a realsystem as explained below:

-   -   Channel model: real wireless systems experience time varying        fading, which is often modeled as a Rayleigh or Ricean process.        In the presence of fading one can obtain multi-user diversity        gains by scheduling a user when his channel is strong. For        channels that offer large multi-user diversity gains,        superposition coding may not provide significant performance        improvements. Therefore one should expect to see larger benefits        of SC in Ricean channels with a large K factor, than in Rayleigh        faded channels.    -   Asymmetry between users: as explained above, superposition        coding and scheduling can provide significant system performance        improvement when the users have very asymmetric channels. In        practice, the level of asymmetry may be limited by various        practical system constraints. For example, the receiver front        end may impose a maximum SINR (e.g., 13 dB in a system such as        1×EV-DO). In addition, a minimum required SINR may be imposed        for the transmission at the lowest possible rate (e.g., −11.5 dB        in 1×EV-DO system). These constraints therefore limit the SINR        span of any 2 users. Furthermore, there is a finite number of        users in each sector, all of which need to be served in a fair        way. This factor may further limit the possible choice of pairs        of users. Accordingly, it may not always be possible to schedule        2 users with very asymmetric channel conditions.    -   Non-ideal interference cancellation: it has been assumed that        the signal of the weak user (e.g., the user with low SNR) could        be completely removed from the received signal of the strong        user (e.g., the user with high SNR). This requires almost        perfect knowledge of the channel fading gain of the strong user,        and almost perfect decoding of the weak user packet. In        practice, the channel fading coefficient is estimated, and        channel estimation error adds a noise term that degrades the        channel SINR. Furthermore, even assuming that perfect decoding        of the weak user packet may be performed, non-negligible        decoding delay may produce hybrid ARQ losses for the strong        user.    -   Coding: the AWGN results used Gaussian channel capacity to        evaluate performance. In practice, the system has a finite set        of modulation schemes and coding rates, and therefore there is        less freedom in the choice of rate pairs and power allocations.

Continuing with the present description, FIG. 2 is a block diagram of acommunication system 200 in which the teachings of the present inventionare implemented. As shown in FIG. 2, the system 200 includes varioususer terminals (UT) 210 and base stations (BS) 220. User terminals 210are also referred to as user stations, remote stations, subscriberstations, or access terminals herein. The user terminals 210 can bemobile (in which case they may also be referred to as mobile stations)or stationary. In one embodiment, each base station 220 can communicatewith one or more user terminals 210 on a communication link calledforward link. Each user terminal 210 can communicate with one or morebase stations 220 on a communication link called reverse link, dependingon whether the respective user terminal 210 is in soft handoff. As shownin FIG. 2, the system 200 further includes a base station controller(BSC) 230 to coordinate and control data communication between the userterminals 210 and the base stations 220. As shown in FIG. 2, the basestation controller 230 may be connected to a circuit-switched network(e.g., PSTN) 290 through a mobile switching center (MSC) 270 and/or apacket-switched network (e.g., IP network) 250 via a packet data servicenode 240 (also referred to as packet network interface herein). Asdescribed herein, in one embodiment, each base station 220 may include ascheduler (not shown) to coordinate and schedule data transmissions fromthe respective base station 220 to the various user terminals 210 thatare served by the respective base station 220. In another embodiment,the scheduler may be implemented within the BSC 230 to coordinate andschedule data transmissions for all base stations 220 that are connectedto the BSC 230. In other words, the location of the scheduler may bechosen depending upon whether a centralized or distributed schedulingprocessing is desired.

FIG. 3 is a diagram illustrating a structure of the forward link 300, inaccordance with one embodiment of the present invention. As shown inFIG. 3, the forward link 300 includes pilot channel 310, medium accesscontrol (MAC) channel 320, control channel 330, and traffic channel 340.The MAC channel 320 includes three subchannels: reverse activity (RA)channel 322, DRCLock channel 324, and reverse power control (RPC)channel 324.

FIG. 4 is a diagram illustrating a structure of a reverse link, inaccordance with one embodiment of the present invention. As shown inFIG. 4, the reverse link 400 includes access channel 410 and trafficchannel 420. The access channel 410 includes a pilot channel 412 and adata channel 414. The traffic channel 420 includes a pilot channel 430,a medium access control (MAC) channel 440, acknowledgement (ACK) channel450, and data channel 460. The MAC channel 440, in one embodiment,includes a reverse rate indicator (RRI) channel 442 and data ratecontrol (DRC) channel 444.

FIG. 5 is a block diagram showing a rate control configurationimplemented in the system shown in FIG. 1, according to one embodimentof the invention. Rate control may also be referred to as linkadaptation herein. Basically, rate control or link adaptation refers tothe process of allocating or changing the transmission rate in responseto channel variations (e.g., changes in signal quality received at theuser terminal). In a system configuration as shown in FIG. 2, the basestations or sectors transmit pilot signals on the pilot channel of theforward link. The user terminals measure the SINR of the pilot signalsreceived from the base stations and predict the SINR for the next packetbased on the measured SINR. The user terminals then request the highesttransmission rate that they can decode based on the predicted SINR for agiven error performance (e.g., a packet error rate (PER)). The raterequests therefore correspond to the signal quality level of datareceived at the user terminals. The rate requests are sent on the DRCchannel on the reverse link to the respective base stations. Asdescribed herein, the rate requests or DRC information are used by thescheduler in accordance with one embodiment of the invention to performthe scheduling functions (e.g., selecting the appropriate user terminalsto receive data transmission from the base station at any given moment).

As shown in FIG. 5, the rate control or link adaptation scheme employedin accordance with one embodiment of the present includes an inner loopand an outer loop. The pilot signals transmitted from the base stationor serving sector 510 are received at the user terminal. The channelpredictor unit 520 measures the received pilot SINR and predicts theSINR for the next packet. SINR prediction is provided to the rateselection unit 550 which selects the highest data rate (DRC) subject toa threshold PER. In one embodiment, as the base station decides to servea particular user terminal with traffic data, the base station transmitsdata to the user terminal at the rate indicated by the most recentlyreceived DRC from the terminal. The outer loop adjusts the SINRthresholds of the data rates based on the error rate of the forwardtraffic channel physical layer packets. As shown in FIG. 5, the packetprocessing unit 540 provides error statistics (e.g., CRC statistics) tothe SINR threshold adjustment unit 530 which adjusts the SINR thresholdsbased on the error statistics and provides the SINR thresholdinformation to the rate selection unit 550. It should be understood byone skilled in the art that the rate control scheme illustrated in FIG.5 is just one example of various rate control schemes that may beimplemented. Similarly, the use of the DRC channel to convey ameasurement of the channel SINR is just one example of various ways toprovide signal quality measurements from the user terminals to theserving base station. For example, in various embodiments, signalquality measurements corresponding to the channel conditions (e.g.,channel SINR) may be quantized and provided to the base stations on adifferent channel. Table 1 illustrates an exemplary mapping between thevarious DRC indices, SINRs, and transmission rates to achieve a certainpacket error rate (e.g., 1% packet error rate). TABLE 1 SINR Rate (bps)DRC Index Threshold (dB) 2.456M 12 9.7 1.843M 11 7.5 1.228M 10 3.81.228M 9 3.7 921.6K 8 1.8 614.4K 7 −0.8 614.4K 6 −0.6 307.2K 5 −3.8307.2K 4 −3.9 153.6K 3 −6.8  76.8K 2 −9.6  38.4K 1 −12

FIG. 6 shows a block diagram of a scheduler 600 in accordance with oneembodiment of the present invention. As mentioned above, the schedulermay be located in the base station or the base station controller,depending upon the particular implementations and applications of thepresent invention. As shown in FIG. 6, the scheduler 600 is configuredto receive signal quality information (e.g., DRC messages) from thevarious user terminals. In one embodiment, the scheduler also receivesother types of information such as queue information and quality ofservice (QoS) information associated with the various user terminalsbeing served by the respective base station(s). For example, the queueinformation associated with the various user terminals may indicate theamount of data waiting to be transmitted from the base station to therespective user terminals. QoS information may be used to indicatevarious QoS requirements associated with the user terminals. Forexample, QoS information may be used to indicate the level of servicethat a respective user terminal is associated with, latencyrequirements, transmission priority, etc. An example of a table 700containing the various selection/scheduling criteria that may be used bythe scheduler 600 in performing its corresponding scheduling functionsis shown in FIG. 7, in accordance with one embodiment of the presentinvention. As shown in FIG. 7, each entry in the table 700 may include auser terminal identifier and the associated signal quality indicator(e.g., DRC index). Table 700 may further includes other types ofinformation associated with the user terminals such as queue informationand QoS information that may also be used by the scheduler to performthe scheduling functions.

In one embodiment, the various types of information provided to thescheduler 600 may be used by the scheduler 600 as selection/schedulingcriteria 610 to select the user terminals for receiving datatransmissions from the serving base station(s). As shown in FIG. 6, thevarious selection/scheduling criteria 610 are inputted to theselection/scheduling unit 620 to select the particular user terminals toreceive data transmission from the serving base station(s) at any givenmoment. The various scheduling methods and algorithms used in variousembodiments of the present invention are described in details below.

In one embodiment, to implement superposition coding and scheduling in amulti-user system such as the system shown in FIG. 2 above, thescheduler 600, for each time interval or time slot, selects two users toreceive data transmissions from the base station and the correspondingpower allocation α. In one embodiment, the choice of users and powerallocation is done in such a way as to maximize a given performancemetric. For example, the proportional fair scheduler used in a systemsuch as 1×EV-DO tries to maximize the product of the throughputs of theusers, where the throughputs are computed in a given time window. In thepresent example, let

-   -   K=number of users    -   t_(c)=scheduler time constant    -   γ_(i)(t)=SNR of user i    -   R_(i)(t)=data rate for user i at time t    -   T_(i)(t)=average throughput of user i at time t        ${T_{i}\left( {t + 1} \right)} = {{\left( {1 - \frac{1}{t_{c}}} \right){T_{i}(t)}} + {\frac{1}{t_{c}}{R_{i}(t)}}}$    -   α_(i)(t)ε[0,1]=fraction of power allocated to user i at time t    -   ƒ_(i)(t)=1 (user I chosen as the strong user—high SNR user),        where 1(.) is the indicator function    -   g_(i)(t)=1 (user I chosen as the weak user—low SNR user)    -   C(SNR)=capacity as a function of SNR        ${R_{i}(t)} = {\left\lbrack {{f_{i}(t)} + {g_{i}(t)}} \right\rbrack{C\left\lbrack \frac{{\alpha_{i}(t)}\quad{\gamma_{i}(t)}}{{\left( {1 - {\alpha_{i}(t)}} \right)\quad{g_{i}(t)}\quad{\gamma_{i}(t)}} + 1} \right\rbrack}}$

In one embodiment, the scheduling problem that optimizes theproportional fair metric can be formulated as follows:${{Maximize}\quad{\sum\limits_{i = 1}^{K}{\log\left\lbrack {T_{i}\left( {t + 1} \right)} \right\rbrack}}},$where the optimization variables are {α_(i)(t)}_(i=1) ^(K) and aresubject to the constraint of being non-zero for at most 2 users.

The solution of this optimization problem requires the computation ofthe optimum power allocation for each of the possible (₂ ^(K)) pairs ofusers, and then the comparison of the corresponding metrics. While it ispossible to solve this problem optimally, various alternative heuristicalgorithms as described below may be used which have a much lowercomputational complexity.

In the present discussion, the problem of choosing the optimal powerallocation is considered for a given pair of users, which WLOG named 1and 2 [what is WLOG?], with γ₁≧γ₂. It is assumed that the capacityfunction has the formC(SNR)=log(1+SNR/G),where G≧1 is some constant that accounts for losses in a practicalcoding scheme. Letting α₁=α and α₂=(1−α), the respective data rates areachieved as follows: $\begin{matrix}{{R_{1}(\alpha)} = {\log\left( {1 + \frac{\alpha\quad\gamma_{1}}{G}} \right)}} \\{{R_{2}(\alpha)} = {{\log\left( {1 + \frac{\left( {1 - \alpha} \right)\quad\gamma_{2}}{\left( {{\alpha\quad\gamma_{2}} + 1} \right)G}} \right)}.}}\end{matrix}$Accordingly, the function to maximize is as follows:ƒ(α)=log(T ₁ +R ₁(α)Δt)+log(T ₂ +R ₂(α)Δt),where Δt=1/(t_(c) −1). Assuming t _(c)>>1, ƒ(α) can be approximated asfollows:${{f^{\prime}(\alpha)} \approx {{\frac{R_{1}^{\prime}(\alpha)}{T_{1}}\Delta\quad t} + {\frac{R_{2}^{\prime}(\alpha)}{T_{2}}\Delta\quad t}}},$which can be set equal to zero and solved for α. The resulting quadraticexpression αα²+bα+c=0 has the following coefficients: $\begin{matrix}{a = {\gamma_{2}^{2}\left( {1 - \frac{1}{G}} \right)}} \\{b = {{2\quad\gamma_{2}} - {\frac{T_{1}}{T_{2}}\frac{\gamma_{2} + \gamma_{2}^{2}}{G}} + \frac{\gamma_{2}\left( {\gamma_{2} - 1} \right)}{G}}} \\{c = {1 + \frac{\gamma_{2}}{G} - {\frac{T1}{T2}\frac{\gamma_{2} + \gamma_{2}^{2}}{\gamma_{1}}}}}\end{matrix}$and can be solved to obtain 2 values of α. These 2 values together with0 and 1 are tested for optimality in the objective function ƒ(α). Itshould be noted that αε[0,1], so any value that falls out of theinterval is discarded.

Continuing with the present discussion, the following heuristicalgorithms may be used to solve the above optimization problem in anapproximate way:

Heuristic Algorithm 1

In one embodiment of the invention, the following algorithm or methodmay be used to select users and schedule data transmissions to optimizea given performance metric (e.g., proportional fair metric):

-   -   Fix a threshold θ that is used to separate strong users (e.g.,        users having high SNR) and weak users (e.g., user having low        SNR). For example, θ can be chosen in the range from 0 to 10 dB.    -   At each time t separate the K users into 2 groups by comparing        their current γ_(i)(t) to the threshold θ.    -   Select one user from each group using an established selection        algorithm (e.g., the standard proportional fair algorithm).    -   Choose the power allocation α between the 2 chosen users as        described above.

The algorithm/method described above is used to schedule at each timeinterval t 2 users with asymmetric channel conditions so as to maximizethe throughput improvement achieved by superposition coding (SC). At thesame time, this algorithm is fair in the proportional fair sense bychoosing the user of each group using the proportional fair algorithm,and choosing the power allocation athat maximizes the proportional fairmetric.

Heuristic Algorithm 2

In another embodiment of the invention, the following algorithm/methodcan be used to select users and schedule data transmissions to optimizea given performance metric (e.g., proportional fair metric):

-   -   Select one user out of the K users using the proportional fair        algorithm.    -   Sequentially consider a second user from the remaining K−1 users        and compute the optimal power allocation α as described above.    -   Select a second user to maximize ƒ(α) as defined above.

As it can be seen from the above description, this algorithm chooses thefirst user in a fair way (in a proportional fair sense) and then basedon this first choice, chooses the second user optimally according to theproportional fair metric.

Heuristic Algorithm 3

In yet another embodiment of the invention, the following algorithm ormethod may be used to select users and schedule data transmissions tooptimize a given performance metric (e.g., proportional fair metric):

-   -   Select one user (first user) out of the K users using the        proportional fair algorithm.    -   Select second user from the remaining K−1 users to maximize the        metric R_(i)/<R_(i)> where <R_(i)> is an average rate computed        using an IIR order 1 filter with time constant t_(c).    -   Choose power allocation α as described above.

In this case, the choice of the first user maximizes fairness while thechoice of the second user is made to exploit multi-user diversity gainby selecting a user with a good channel condition. Fairness is againachieved by choosing the power allocation α to maximize the proportionalfair metric.

FIG. 8 is a diagram illustrating a transmission scheme on the forwardlink in accordance with one embodiment of the present invention. Incontrast with the conventional TDM scheduling and transmission schemementioned above (e.g., the forward link TDM scheduling and transmissionin the current IS-856 system), a system in accordance with oneembodiment of the invention can schedule data transmission for multiple(e.g. two) users at any given time to improve the system throughput andperformance. As shown in FIG. 8, for any given time interval, the systemselects and schedules data transmission for two users as describedabove. Instead of wasting a significant amount of bandwidth to serve oneuser at a time, especially those users with low SINR, the system invarious embodiments of the invention selects and schedule multiple(e.g., two) users for data transmission to optimize a given performancemetric (e.g., the proportional fair metric). For example, by selectingtwo users, one with very high SINR and another with low SINR andtransmitting to these two users simultaneously, the base station avoidsthe need to partition its bandwidth between the two users. Thus, thebase station resources are more fully utilized and the system throughputis significantly improved. Referring again to the example shown in FIG.8 in which two users are selected in any given time interval, user 1 anduser 9 are served during time interval T1, user 2 and user 11 are servedduring time interval T2, and so on.

In one embodiment, as described herein, after the scheduler has selectedmultiple (e.g., two) users to receive data transmissions from the basestation, a multi-user packet is constructed which carries higher layerdata for the multiple users. In one embodiment, the multi-user packet(called first packet in this example) contains application data for oneof the users (e.g., the user with low SINR) and control information(signaling data) for the other users (users with higher SINR). Anotherpacket (called second packet in this example) is then super-imposed uponthe multi-user packet. The second packet contains the application datafor the user having SINR. In one embodiment, the second packet is codedso that it behaves like random interference with respect to themulti-user packet.

FIG. 9 shows an example of a multi-user packet in accordance with oneembodiment of the present invention. Various formats of multi-userpackets are described in commonly assigned U.S. patent application Ser.No. 10/368,887, entitled “Variable Packet Lengths for High Packet DataRate Communications,” filed Feb. 3, 2003. As shown in FIG. 9, themulti-user packet 910 is a single physical layer packet which containshigher layer payloads addressed to multiple users. In this example, themulti-user packet 910 contains multiplexed MAC layer packet, formatfield (FMT), CRC, and tail bits. In one embodiment, the FMT value (e.g.,“00”) is used to indicate that the physical layer (PL) packet is amultiplexed packet. The MAC layer packet is formed from two SecurityLayer (SL) packets and an inner CRC. Each SL packet has a correspondingMAC ID value (e.g., 5 for SL Packet 1 and 7 for SL Packet 2. Each SLpacket is appended with a SubPacket Identification (SPID) field and aLENgth indicator (LEN) field. It should be understood by one skilled inthe art that this is just one example of various formats that may beused to construct a multi-user packet and that the teachings of thepresent invention should not be limited to any particular format ormeans used in constructing a multi-user packet which contains higherpayloads addressed to different users.

FIG. 10 shows an example of a multi-user packet upon which anotherpacket is superimposed. As shown in FIG. 10, the multi-user packet inthis case is a single physical layer packet which contains higherpayloads for two users (e.g., user 1 with high SINR and user 2 with lowSINR). In this example, the multi-user packet (also referred to as firstpacket in this example) contains application data for user 2 andsignaling data for user 1. In one embodiment, signaling data or controlinformation addressed to user 1 may contain coding, modulation, andscrambling parameters, etc., associated with another physical layerpacket (also referred to as second packet in this example) that issuperimposed on the multi-user packet and transmitted simultaneouslywith the multi-user packet. The multi-user packet is constructed andsent at a data rate which is low enough so that both users candemodulate. Upon receipt of the signaling data embedded in themulti-user packet, the high SINR user subtracts the contribution of themulti-user packet from the received signal, and uses the resultingsignal to extract the second packet, whose encoding parameters werespecified by the signaling data. Thus, the low SINR user is served bythe bulk of the multi-user packet, while the high SINR user is served bythe second packet that was superimposed on the multi-user packet.

FIG. 11 is a flow diagram of a method for data transmission in awireless communication system, in accordance with one embodiment of thepresent invention. As described in FIG. 2 above, the communicationsystem in this example may include one or more base stations. Each basestation may serve a number of user stations. At block 1110, signalquality indications are received from one or more user stations that arebeing served by a first base station. As mentioned above, each userstation may measure signal quality of signals received from the firstbase station and transmit a request for a particular transmission rate(e.g., a DRC message) based on the measured signal quality to the firstbase station. Again, in other embodiments, the user stations maycommunicate signal quality measurements to the base station in otherformats (e.g., quantized SINR values, etc.). In one embodiment, thesignal quality indications (e.g., DRC messages) received from the userstations are used by a scheduler/controller to select multiple stations(e.g., a first user station and a second user station) to receive datatransmissions from the first base station (at block 1120). As mentionedabove, various algorithms or methods may be used to select the multiple(e.g., two) user stations in order to optimize a given performancemetric (e.g., the proportional fair metric). In one embodiment, one ofthe two user stations selected (e.g., the first user station) has arelatively high signal quality and the other user station (e.g., thesecond user station) has a relatively low signal quality. Again, invarious embodiments of the present invention, other types of informationmay also be taken into consideration in selecting the user stations.Such information may include, for example, queue information and qualityof service (QoS) information. At block 1130, a multi-user packet (calledfirst packet in this example) is constructed which contains controlinformation or signaling data for the first user station and applicationdata for the second user station. At block 1140, a second packetcontaining application data for the first user station is super-imposedupon the first packet. At block 1150, the first and second packets aretransmitted simultaneously from the first base station to the first andsecond user stations.

FIG. 12 is a flow diagram of a method for data processing in a wirelesscommunication system, in accordance with one embodiment of the presentinvention. At block 1210, first and second packets transmitted from afirst base station is received at a first user station. The first packetis a multi-user packet containing signaling data for the first userstation and application data for a second user station. The secondpacket contains application data for the first user station and issuper-imposed upon the first packet. In one embodiment, the signalingdata in the first packet indicates the coding, modulation, and/orscrambling parameters of the second packet. At block 1220, signalingdata for the first user station is retrieved from the first packet. Inone embodiment, upon receiving the signaling data embedded in themulti-user packet, the first user station subtracts the contribution ofthe multi-user packet from the received signal. At block 1230, the firstuser station uses the signaling data retrieved from the first packet toextract the second packet.

Again, it should be understood and appreciated by one skilled in the artthat the teachings of the present invention can be applied to caseswhere more than users are selected to receive data transmission from thebase station in any given time interval. In the general case, themulti-user packet is sent at a data rate indicated by the packetpreamble, and is decoded by all users whose SNR is sufficient to decodethe packet. Upon successful decoding, the users parse the physical layerdata to extract any higher layer payload that may be addressed to them,and discard the rest of the physical layer packet.

For example, let 1, 2, . . . , K denote the users who are currentlyscheduled by the superposition coding scheduling, in the decreasingorder of channel SNR. In one embodiment, the codeword c_(K) that ismeant for the user with the lowest SNR is used to encode a multi-userpacket. In this example, the multi-user packet is used to carryapplication data for the K^(th) user, as the well as control informationfor other users, who are being served simultaneously, throughsuperposition coding. As mentioned above, the control information may beused to specify the identity of the other users being served, as well asthe coding, modulation and scrambling parameters associated with theother codewords that are being superimposed with the codeword c_(K).Once the users with channel SNR better than that of the lowest-SNR userdecode the codeword c_(K), the control information contained in thepacket enables the other scheduled users to successively decode andinterference-cancel the remaining packets that are superimposed, untilthey decode the packet that contains application data meant for them.

Thus, in various embodiments of the invention as described in theexample above, there can be multiple (e.g., M packets) superimposedtogether. In one embodiment, the lowest level packet may containcontrol/signaling information about all the higher level packets. Inthis case, only the lowest level packet needs to be a multi-user packet.The other packets may be either single user packets or multi-userpackets, depending on various applications and implementations of theinvention. Once the superimposed M packets are received, they can bedecoded as described above by the respective users to extract theapplication information intended for them.

Alternatively, in another embodiment, the multiple packets may besuperimposed together as follows. A packet at each level may containcontrol/signaling information (e.g., coding, modulation, block-length,etc.) about the packet at the next higher level. In this embodiment, thelower level packets are multi-user packets while the packet at thehigher level may or may not be a multi-user packet. As an example, thehighest level packet may contain application data for multiple users, athigh SNR.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method for processing data in a communication system, comprising:receiving indications of signal quality associated with a plurality ofuser stations; selecting a first user station and a second user stationto receive data from a base station, based on the indications of signalquality; constructing a first packet containing signaling data for thefirst user station and application data for the second user station;super-imposing a second packet upon the first packet, the second packetcontaining application data for the first user station; and transmittingthe first and second packets simultaneously from the base station to thefirst and second user stations.
 2. The method of claim 1 furthercomprising: receiving the first and second packets at the first userstation; retrieving signaling data for the first user station from thefirst packet; and extracting application data for the first user stationfrom the second packet using the signaling data retrieved from the firstpacket.
 3. The method of claim 2 wherein the signaling data containsinformation processing parameters used by the first user station toprocess the application data in the second packet.
 4. The method ofclaim 3 wherein the information processing parameters include coding andmodulation parameters.
 5. The method of claim 1 wherein the indicationof signal quality associated with each user station corresponds to asignal to noise plus interference ratio (SINR).
 6. The method of claim 1further comprising: measuring, at each of the plurality of userstations, quality of signals received from the base station; andcommunicating information representing the measured quality to the basestation.
 7. The method of claim 6 wherein communicating comprises:determining a desired data rate supportable by the respective userstation, based on the measured quality; and sending a message indicatingthe desired data rate from the respective user station to the basestation.
 8. The method of claim 7 wherein the indication of signalquality associated with each user station corresponds to the desireddata rate requested by the respective user station.
 9. The method ofclaim 1 wherein a table is used to keep track of the indications ofsignal quality associated with the plurality of user stations.
 10. Themethod of claim 8 wherein the first user station has a relatively higherdesired data rate compared to the second user station.
 11. An apparatusfor processing information, comprising: a receiver to receiveindications of signal quality associated with a plurality of userstations; a controller to select, from the plurality of user stations, afirst user station and a second user station to receive data from a basestation based on the indications of signal quality; and a transmitter totransmit a first packet and a second packet that are superimposedtogether to the first and second user stations, the first packetcontaining signaling data for the first user station and applicationdata for the second user station, the second packet containingapplication data for the first user station.
 12. The apparatus of claim11 wherein the first user station, upon receiving the first and secondpackets, retrieves the corresponding signaling data from the firstpacket and extracts application data from the second packet using thesignaling data retrieved from the first packet.
 13. The apparatus ofclaim 12 wherein the signaling data contains information processingparameters used by the first user station to process the applicationdata in the second packet.
 14. The apparatus of claim 13 wherein theinformation processing parameters include coding and modulationparameters.
 15. The apparatus of claim 11 wherein the signal qualityassociated with each user station corresponds to a signal to noise plusinterference ratio (SINR).
 16. The apparatus of claim 11 wherein thesignal quality associated with each user station is measured based on apilot signal received from the base station.
 17. The apparatus of claim11 wherein each user station, based on the signal quality measured atthe respective user station, communicates to the base station a desireddata rate for data transmission from the base station to the respectiveuser station.
 18. The apparatus of claim 18 wherein a table is used tokeep track of the indications of signal quality associated with theplurality of user stations.
 19. The apparatus of claim 17 wherein thesignal quality associated with each user station corresponds to thedesired data rate for data transmission requested by the respective userstation.
 20. The apparatus of claim 19 wherein the first user stationhas a relatively higher desired data rate compared to compared to thesecond user station.
 21. An apparatus for processing data in acommunication system, comprising: means for receiving indications ofsignal quality associated with a plurality of user stations; means forselecting a first user station and a second user station to receive datafrom a base station based on the indications of signal quality; meansfor constructing a first packet containing signaling data for the firstuser station and application data for the second user station; means forsuper-imposing a second packet upon the first packet, the second packetcontaining application data for the first user station; and means fortransmitting the first and second packets simultaneously from the basestation to the first and second user stations.
 22. The apparatus ofclaim 21 further comprising: means for receiving the first and secondpackets at the first user station; means for retrieving signaling datafor the first user station from the first packet; and means forextracting application data for the first user from the second packetusing signaling data retrieved from the first packet.
 23. The apparatusof claim 7 wherein the indication of signal quality associated with eachuser station is communicated to the base station as a desired data ratefor data transmission from the base station to the respective userstation.
 24. The apparatus of claim 23 wherein a table is used to keeptrack of the desired data rates requested by the plurality of userstations.
 25. A communication system comprising: a base station; aplurality of user stations to communicate with the base station via acommunication link, wherein the base station to select, among theplurality of user stations, at least two user stations including a firstuser station and a second user station to receive data from the basestation based on data rates for data transmission supportable by each ofthe plurality of user stations, the base station to simultaneouslytransmit a first packet and a second packet that are superimposedtogether to the first and second user stations, the first packetcontaining signaling data for the first user station and applicationdata for the second user station, the second packet containingapplication data for the first user station.
 26. The communicationsystem of claim 25 wherein the first user station, upon receiving thefirst and second packets, retrieves the corresponding signaling datafrom the first packet and extracts application data from the secondpacket using the signaling data retrieved from the first packet.
 27. Thecommunication system of claim 25 wherein the data rates supportable byeach user station corresponds to quality of signals received at eachuser station.
 28. The communication system of claim 25 wherein thequality of signals received at each user station corresponds to a signalto noise plus interference ratio (SINR) measured at the respective userstation.
 29. The communication system of claim 25 wherein a table isused to keep track of the data rates associated with the plurality ofuser stations.
 30. A machine-readable medium comprising instructionswhich, when executed by a machine, cause the machine to performoperations including: selecting, from a plurality of user stations, afirst user station and a second user station to receive data from a basestation based on quality of signals received at the first and seconduser stations; constructing a first packet containing signaling data forthe first user station and application data for the second user station;super-imposing a second packet upon the first packet, the second packetcontaining application data for the first user station; and transmittingthe first and second packets simultaneously from the base station to thefirst and second user stations.
 31. The machine-readable medium of claim30 wherein the operations performed further including: receiving thefirst and second packets at the first user station; retrieving signalingdata for the first user station from the first packet; and extractingapplication data for the first user station from the second packet usingsignaling data retrieved from the first packet.
 32. The machine-readablemedium of claim 30 wherein the quality of signals received at each userstation corresponds to a signal to noise plus interference ratio (SINR)measured at the respective user station.
 33. The machine-readable mediumof claim 29 wherein the quality of signals received at each user stationcorresponds to a data rate requested by the respective user station fordata transmission from the base station to the respective user station.34. A method for processing data, comprising: receiving indications ofsignal quality associated with a plurality of user stations; selecting,from the plurality of user stations, a set of K user stations to receivedata from a base station, based at least in part on the indications ofsignal quality received; and transmitting multiple packets that aresuperimposed together from the base station to the K user stations. 35.The method of claim 34 wherein a packet at the lowest level in thesuperimposed packets comprises a multi-user packet containingapplication information for a first user station having the lowest levelsignal quality in the set and control information for other userstations in the set.
 36. The method of claim 35 further comprising:receiving the superimposed packets at a second user station; retrievingcontrol information for the second user station from the lowest levelpacket in the received superimposed packets; and extracting applicationinformation intended for the second user station from remaining packetsin the received superimposed packets.
 37. The method of claim 34 whereina packet at a lower level in the superimposed packets contains controlinformation for a packet at a next higher level in the superimposedpackets.
 38. The method of claim 37 wherein the packet at the lowerlevel in the superimposed packets comprises a multi-user packetcontaining application data for a corresponding user and controlinformation for another user at a next higher level.
 39. The method ofclaim 37 wherein a packet at the highest level in the superimposedpackets comprises a multi-user packet containing application data formultiple user stations in the set.
 40. An apparatus for processinginformation, comprising: a controller to select, from a plurality ofuser stations, a set of multiple user stations to receive data from abase station based at least in part on indications of signal qualityassociated with the plurality of user stations; and a transmitter totransmit multiple packets superimposed together to the multiple userstations.
 41. The apparatus of claim 40 wherein a packet at the lowestlevel in the superimposed packets comprises a multi-user packetcontaining application information for a first user station having thelowest level signal quality in the set and control information for otheruser stations in the set.
 42. The apparatus of claim 40 wherein a seconduser station, upon receiving the superimposed packets, retrieves controlinformation for the second user station from the lowest level packet inthe received superimposed packets and extracts application informationintended for the second user station from remaining packets in thereceived superimposed packets.
 43. The apparatus of claim 40 wherein apacket at a lower level in the superimposed packets contains controlinformation for a packet at a next higher level in the superimposedpackets.
 44. The apparatus of claim 43 wherein the packet at the lowerlevel in the superimposed packets comprises a multi-user packetcontaining application data for a corresponding user and controlinformation for another user at a next higher level.
 45. The apparatusof claim 43 wherein a packet at the highest level in the superimposedpackets comprises a multi-user packet containing application data formultiple user stations in the set.
 46. A method for processing data,comprising: receiving multiple packets that are superimposed together ata first user station, the multiple packets including a first packet anda second packet; retrieving signaling data for the first user stationfrom the first packet; and extracting application data for the firstuser station from the second packet using the signaling data retrievedfrom the first packet.
 47. The method of claim 46 wherein the signalingdata contains information processing parameters used by the first userstation to process the application data in the second packet.
 48. Themethod of claim 47 wherein the information processing parameters includecoding and modulation parameters.
 49. An apparatus for processing data,comprising: a receiver to receive multiple packets that are superimposedtogether, the multiple packets containing a first packet and a secondpacket; a decoder to decode the multiple packets, the decoder toretrieve signaling data for a first user from the first packet andextract application data for the first user from the second packet usingthe signaling data retrieved from the first packet.
 50. The apparatus ofclaim 49 wherein the signaling data contains information processingparameters used by decoder to process the application data contained inthe second packet.